Ultrasonic nondestructive testing apparatus and control therefor



Oct. 24, 1961 D. c. ERDMAN 3,005,335

uLTRAsoNIc NoNnEsTRucTIvE TESTING APPARATUS AND CONTROL THEREFOR 4 Shee'ts-Sheel 1 Filed May l, 1957 INVENTOR.

Oct. 24, 1961 D. c. ERDMAN ULTRAsoNIc NoNDEsTRUcTIvE TESTING APPARATUS AND CONTROL THEREFOR 4 Sheets-Sheet 2 Filed May 1, 1957 Oct. 24, 1961 D. c. ERDMAN ULTRAsoNIc NoNDEsTRUCTIvE TESTING APPARATUS AND CONTROL THEREFOR 4 Sheets-Sheet A3 Filed May 1, 1957 mm|hu|| Oct. 24, 1961 Filed May 1.` 1957 FEEQ '/YLC.

VOLTHGE VOLTHGE VQLTH 6E voLmeE D. c. ERDMAN 3,005,335 ULTRAsoNIc NoNDEsTRUcTIvE TESTING APPARATUS AND CONTROL THEREFOR 4 Sheets-Sheet 4 INVENTOR.-

DOA/HAD C. {Po/wan .United States Patent This invention relatesv to ultrasonic nondestructive'testing apparatus, and, more particularly, to ultrasonic apparatus which may be used in the nondestructive testing of materials to detect hidden flaws, measure thicknesses of materials, and the like, wherein propagation time 0f ultrasonic waves is measured. l

The invention presents various control arrangements for improving the indications or displays produced by apparatus for determining the 'propagation time along a predetermined path.

The purpose, of my inventionis to provide a visual indication of any awsor defects that might be present in an object under test even though the defects are located beneath the exterior surface portion of the object and are not normallyr visible.

A further object is to provide such visualindicaton in a nondestructive manner so that the object being tested is not attested in any way.

'In accordance with the arrangement of the present invention, a variable-voltage source is employed to produce a range sweep signal in the form of voltage excursions Which change in a predetermined manner with respect to time. By way of example, the range sweep v'sig-` nals may have a wave form of saw-tooth'shape. Alter'- nate electrical signals are generated each having la fre-l quency which varies continuously and cyclically over ia determined olset range of frequencies.' These electrical signals when applied lto a transducer provide a plurality. of ultrasonic waves whichare'transmitted during each range sweep. The frequency of the ultrasonic waves cor' responding to the electrical signals varies continuously vand cyclically o ver a determined range V of frequency which may vary from a rate to a maximum ratejor vice versa. The echo signals which are produced by the' transmitted signals and reflected by the object/and defects therein are detected and'rnixedwith the electrical signal then being generated. Thiseproduc'es'fvideo signals which represent the time of occurrence of the echo signals'which are detected. The video signal is combined with the range sweep signal-to produce a control signalhaving a slope which varies in accordance with the fslope ofthe voltage excursions of the rangefsweep signal 4during periods of time when -no video signals occur and having a slope which `isreduced during-the periods of time when video signals do occur. This ncontrol signal may beenrployed in various manners to improve the indications or displays which are produced by the apparatus.

An advantage 'of the present invention is toprovide novel means for improving the resolution of images which are produced on the cathode-ray tube by the ultrasonicA apparatus. f.

Another advantage of the invention is 'the Yinclusion of an addition circuit whereby the variable voltage source is combined with an output signalfrornY .fvideeamqelierffe to improvethe resolution of the display.y Y

` The present invention contemplates n'ovel apparatus for` the nondestructive testing of materials and includes various arrangements of combining, by means of an addition circuit, the output ofthe video amplifier with the output of aA variable voltage `source ftd-squeeze or compress the signal display for improving the resolution thereof.

The foregoing andother objects vand advantagesof thev invention will appeal-'more fully hereinafter from a conin the voltage excursions.

sweep of ultrasonic apparatus to have two speeds.

FIG. 2 illustrates Ian embodiment 'of the invention wherein the control signal is employed to compress or vsqueeze the respective video signals which are detected as a result of echos produced by a target. FIG. 3 illustrates a modification of the control arrangement of FIG. 2 yfor use with B-type scan displays.

FIG. 4 illustrates the wave forms of signals' which are produced in the apparatus of FIGS. 1 to 4.

FIG. 5 illustrates the wave forms of the signals whichY are involved in the control arrangement'which is the subject matter of this invention.

Referring to the drawings, and, more particularly, t0, FIGS. l, 2 and 3, there are shown combination block and schematic diagrams of the general type shown in my copending and continuation-impart patent V application Serial No. 522,542, filed July 18, 1955 for Methods and Apparatus for Measuring Wave Propagation Time, now U.S. Patent 2,931,978, the inventor and assignee of said copending patent application being the same as the i11-v ventor and assignee ofthe instant application.

In FIG. l there is shown a timing pulse generator 12, which provides a series vof equally spaced pulses A (see wave forms in FIG. 4) which control the sequence of operations in the apparatus. The timing pulse generator is a variable repetition rate type and the rate or period-` icity of the pulses is controlled by the voltage. which is produced by variablevoltage source 14. The variable voltage source 14 may comprise a potentiometer 16 which is connected across asource of potentialV 18 and which is driven by a motor 20, or it may beY a conventional electronic sweep generator which' provides periodic voltage exercursions.

The timingpulses A are applied to a'sweep generator 22 and to a bi-stable circuit 24. The sweep generator produces voltage excursions B (see FIG. '4) having sawtooth wave form in synchronism with the timing pulses A. The `bi-stable circuit produces signals C (see FIG. 4) of rectangular wave form excursions B.

'I'he saw-tooth signals Band the rectangular signals C are applied to a gated addition circuit 26V where they areV summed to provide an output 'signal D (see FIG. V4) of saw-tooth wave form wherein the adjacent voltage excursions start from and follow ditferents'voltage levels.. The addition circuit is provided with anyvariahle con#A ventional means, such as a Vpair of potentiometers for adjusting the slopes of the respective voltage excursions and may be associated withother apparatus, Ysuch as a pair of potentiometers, :for adjusting the amount of offset While any suitable or conventional apparatus maybe used for this additionv circuit, thepotentio'metersrotheadditon 'circuit 26 may be em ployed as specifically set forth inthe aforementioned co'- pending patent application.

The output signal of laddition circuit 2 6 is' applied -to a reactance tube circuit 36. Theoutput of the reactance tube circuit is applied to an oscillator 38 and it serves to cause the oscillator to produce the waves whichoccur in time sequence and-'whichhave frequencies which vary or sweep periodically inithe sarne manner insynchronism with` the voltage excursions ofthe signals D which are in synchronism with the voltage produced by the addition circuit. The second wave (in time) is offset in frequency from the first wave an amount which is proportional to the offset in the voltage excursions D. The output signals of the oscillator are applied through a power amplifier 66 which isa variableV gain so that'a signal havingthe general wave form of F F-IG. 4) is connected to a crystal or other transducer 44, which serves to transmit and receive ultrasonic signals, with said crystal beingconnected to ground in theconventional manner as shown by symbol. As illustrated in thewave form F of FIG. 4, the amplitude of the signal which is conveyed through the power amplifier 66 is reduced during alternate cycles of operation, and the wave of reduced amplitude is mixed with the echo ,signals in the amplifier 52 to provide heterodyne signals.

In conventional practice, the transducer has a portion thereof immersed in liquid which serves to convey the ultrasonic waves with much greater efficiency than would be possible in the air, The output of the power amplifier 66 is fed into transducer 44 and simultaneously into the amplifier 52. The echo signals which are received by the transducer 44 are also fed into the amplifier 52. The out. put of the amplier 52 has a wave form G (see FIG. 4) which is fed through a narrow band filter 56, thence through a detector 58, and a video amplifier 60.

The narrow band filter 56 may be arranged to pass hcterodyne signals having any desired frequency. By way of example, the filter 56 may be tuned to pass signals having a frequency of 455 kilocycles. Such filters are readily available because they are conventional types.

The detected signal is amplified by a video amplifier 66 and applied to one set of the deection plates of a cathoderay tube represented as an indicator 62. The variable voltage which is produced by the source 1.4 is applied to the other set of the deflection plates of the cathode-ray tube or indicator 62. Such a deflection arrangement provides an A-type scan so that the location of the detected signal along the horizontal axis of the cathode-ray tube provides a measure ofthe distance to the target.

In the operation of the circuit thus described frequency modulated electrical signals are produced and applied to the transducer. These frequency modulated signals vary uniformly and cyclically in frequency in accordance with the wave shapes set forth in wave representation F in FIG. 4. To produce such frequency modulated signals the entire apparatus is synchronized with the output of the variable voltage source 14. The timing pulse generator 12 which is synchonized yby the variable voltage source produces a series of synchonized pulses occurring at a particular repetition rate as shown in wave representation A of FIG. 4. v

In a conventional manner these impulses operate a multivibrator 24 and a sweep generator 22, the outputs of which in turn are added in the addition circuit 276 to produce the wave shape D of FIG. 4. These varying voltages are applied to the reaction tube circuit 36 and oscillator 38 which in turn produces a signal which varies in frequency proportional to the variation of the voltage input.

Therefore, the frequency modulated wave shape F occurring in the time portion Te of FIG. 4 is applied to the transducer which in turn produces proportional ultrasonic waves of uniformly and periodically 4varying frequencies which aretransmitted into the object under test. In the illustrated example shown in FIG. 4 this frequency modulated wave varies in frequency from 4.70 megacycles to 5.0 megacycles.

In the next time portion in FIG. 4 the alternate frequency modulated signal that is produced varies in frequency from 4.455 megacycles to 5.4575 megacycles.

These above-described variations in frequency are repeated periodically.

It should fbe noted that the last mentioned alternate frequency modulated wave occurs at a much smaller arn- Plitnde then the 'tiret mentiened is @ne Vte the ecnnection between the bistable circuit 24 and the power amplifier 66; In operation this alternate signal which is of smaller amplitude is compared to any echo signals that are reflected back from points along the path of t-he signal transmitted during the time period Te. Since the echo Signals eine have a. smaller amplitude, the signals can be more properly compared.

When the signals reflected from a defect are applied to the amplifier 52 with a frequency that is different from the frequency then being supplied from the power amplilier 66 by a preselected amount the resultant difference signal will pass through the narrow band Iilter 56 which has a frequency response of the constant and preselected frequency difference.

Accordingly, by varying the rate of frequency change of the frequency modulated generator or by varying the frequency transY a to determine precisely the location of the defect,

It can accordingly be seen that it is not necessary to indicate. e plurality of eelleen sinlnlteneenslrlf there:

is only onefdefect present one reflection will be indicated on the cathode ray tube.

The distance to the target is also indicated by the time between the pulses which are produced by the timing pulse generator at the instant when a signal appears on the screen of the cathode-ray tube. If desired, the signal which is produced by the variable voltage source 14 may be adjusted manually and the distance to the target may be ascertained by observing the manual setting of the voltage source when a signal is produced on the screen of the cathode-ray tube. However, it is preferable that the signal which is produced by the source 1:4 be varied cylically, as indicated in FIG. '1, so that plural reecting surfaces may be indicated during each cycle of operation.

In FIG. 1 the output of the video amplifier 66, which is connected to one set of the deflection plates of the cathodefray tube 62, is simultaneously connected through an inverter and thence to a second addition circuit 81. The signal from the variable voltage source 14 which is fed to the other set of plates of the cathode-ray tube 62 is simultaneously connected to the addition circuit 81 via one end of a resistor 82. The output of the inverter 80 is connected via the variable resistor 83 to the terminal 84. A resistor 8'5 is connected via ground to the terminal 84 which in turn is connected to the inputv of the timing pulse generator 12.

The wave form 8,6, representative of the output of video amplifier 60, is inverted in inverter 80 to produce the wave form Y. The wave form X is the range sweep signal and is combined with the signals Y to produce the control signals Z, which are fed via the addition ciricuit S1 into thetiming pulse generator 12. Waveforms X, Y, and Z are shown represented in FING.

The control signals Z, in FIG. .1, are employed to control the repetition rate of the pulses A which are produced by the timing pulse generator 12, The signals Z cause the rate of change ofthe repetition lrate of the pulses A to be reduced when video signals are received, thereby decreasing the range sweep rate when video signals are being received.

rIhe wave form X is the range sweep signal, and it may be produced by a motor driven potentiometer as illustrated in the drawings. The signals Y are the video signals which are, predueed et the output et the ultrasonic apparatus and which represent echo infomation. The video Signals Y are inverted SQ that they may be. combined with the range sweep signals in an addition circuit to provide the difference between the instantaneous magnitudes of the signals X and Y. The difference between the signals X and Y is the signal Z having a slope which varies in accordance with the slope of the voltage excursions of the range sweep signal X during periods of time when no video signals occur, and having a slope which is reduced during periods of time ywhen video signals do occur. 'Ihe eetnnressed er squeezed Signals ,are represented in wave:l

tted portion of the filter 56 it is possible form on FIG. 2, adjacent the cathode-ray tube, bearing legend C. R. Tube display. l y' In FIG. 2., there are shown numerous blocks which are similar to those shown in FIG. 1with the like blocks and parts having like reference numerals. The addition ycircuit 81 of FIG. 2 is similar to that shown in FIG. 1, but in 2 the output of the video amplifier 60 is fed simult fneou'sly into'the inverter 80 and to one of the vertical detlecting plates of the cathode-ray tube 62. The output of the inverter 80 is fed into the variable resistor 83, so that theinverter signal Y combines rwith the signal X and"`is fed into one of the horizontal deecting plates of the cathode-ray tube 62. Further, the signal X from the variable voltage source 14 is also fed into the timing pulse generator 12, but directly, as distinguished from FIG. l. -In FIG. 2 the controlsignals'Z Vare applied to the horizontal dellecting circuit of thecathode-r'ay tube to cause the video signals which are displayed on A-Scan to be squeezed or confined to a smaller area. Squeezing of the video signals results because the waveform Z is applied to the horizontal deecting plates of. cathode ray` tube62. With no Z signal appliedhto the cathode ray tube 62 the spot corresponding to the 'electron beam of the cathode ray tube will 'be deected' from left to right, flor example as Ya horizontal line, Vif no video signal is appli/ed to the vertical deectin-g plates. 'If the signal applied to the horizontal plates has an ordinary, sawtooth waveform such as waveform X shown in lFIG. 5 the spot is deilected .across the screen at a constant rate. Therefore any video signalwhich is applied to the vertical plates would appear as a vertical deection of the spot on the cathode ray tube. If a square wave signal Vwere applied to the vertical plates for example, a square wave would appear. on the cathode ray tube. v

`jOn'` the 'other hand thewaveforrnZ applied to the horizontal plates provides a different presentation. As s tatedwhenever a vdeo signal is applied to the vertical dellecting plates of the cathode ray tube Vthe slope of the signal Zfisfhanged to decrease ,the sweep rate of the waveformX at this particular time.'A Therefore, if a square wave were presented the width of the square wave would appear to be much smaller thanV the width of the square .wave with the ordinary sawtooth horizontal sweep voltage.V 'With a lower sweep rate the electron beam will move from.left to right moreslowly and therefore the square wave'will be presented onV a much smaller portion of` the horizontal sweep line and accordingly compressed. wIn FIG. `3there are 'shown numerous blocks which are similantothose shownin FIG. V1,- with like blocks and parts having like referencenumerals. vThe addition circuit 81 of FIG. 3 's similar to that shown in FIG. 1, but in FIG. 3 the output of the video ampliier 60 is fed simultaneously into the inverter 80 and to one of the control grids of the cathode-ray tube 62. The signals X and Y, which are fcombinedinthe, addition circuit 81-provide signals Z which are fedinto one of the ,vertical deecting plates oft-'the cathode-ray tube 62. The signal Xlis also eltintq the'jtiming pulsegenerator 12, as is shown in A stepped testngblock havinga representative aw therein is shown positioned ,belowr a .transducer 44 which may be a crystal. A direct current source of energy 93' a terminal 93 connected to ground.V Amovable terminal 94, movable in relation to the variable resistor 92, moves in response to lateral movement of the transducer 44, as indicated by the arrows positioned immediately below the transducer 44. A motor 91, operable from a suitable control, has a lead screw 95 which is normally connected through a lead nut carried by the transducer 44, so that rotation of the motor 91, in either direction, will cause the lead screw to rotate in the proper direction and move the transducer laterally, accordingly. The signal F is connected to the transducer 44. The signal reected from the object and received bythe transducer` 44 is connected tor the amplifier 52. 'i

As transducer 44 moves 'horizontally across the test block or test piece, a corresponding second. range sweep signal V signal is attained from variableresistor l92, or` on potentiometer, which signal synchronizes the horizontal movement of transducer 444 with the horizontal sweep appearing on cathode-ray ltube 62. v v In FIG. 3 the control signals Z are supplied to the vertical dedection circuit of the cathode-ray tube, causing the video signals which are'displayed-on B-Scan to be squeezed or compressed, thereby producing a sharper image of the dbject and flaws-being scanned. 1 Y

'Ihe well known B-scan is a two dimensional presentation ofthe object scanned. InV practicev the B-scan reveals defects in an objectwith respect to a top andV bottomsurface of the object along a scan length of theobject. Asthe YB-scan presentation is conventional iti-need not bre/described in detail. v Y In the operation of FIG. 3 the range signal Xproduced by the motor driven potentiometerl is combined with the inverted video signal Y'to provide Athe rangeV signal'Z. The range signal Z isY connected'to'thevertical deection plates of cathode ray tube 62 to control the verticalpresentaton of the spot on the tube. In the conventional B-scan presentationV this represents the Y axis or propagation time axis of the two coordinate presentation. V 1 The signal reected fromthe object andthe `then being transmittedsignal Fy arefdetected :and mixed and ampliedin amplifier 52 and transformed intov a video `signal as previously described. d

' f VSimultaneously 'with the "scanning operation Vthey motor driven contact 94 moving overtheresistor `92 produces the signal V in` synchronization with the range sweep' signals X.Vv The signal VS produced by theVv scanning mechanism is a range sweep'signal representing the positionV of the transdcer'44 vas it scans Vthe object 90.V l j l The range sweep signal V is applied to the horizontal deil'ection electrode of the cathode ray tube 62 and corresponds to the X axis orp'scanilength in thejB-s'can:

presentation. v Y l .Asfshown in FIG. 3V the output ofi-video amplifier 60 is also applied to a, control grid of the cathode ray tube 62. The video signal acts to bias thecontrol grid with' respect to the cathode v,of v'the cathoderay tube to provide'` conventional spot intensity modulation of the presentation shown onthe tube. Thus when a video signal produced it is not ,only compressed but employed to biasthe c'ontrol of the cathode ray tube 62 intensifying the spot: r The sombined. compressingfand spot intensity modulation "provides a` presentation, on the cathode ray tube 62.

clear `sharp 'B-'scan presentation of I high resolution.l

From the foregoing it,will4 be seen that there are presented three ditferent'arr'ange'ments employingthe user of special control signals lto improve'the resolution .of the images which produced on the cathttd'e-raytube by the ultrasonic apparatus. The invention may be, rp'lyea with ,either ASC311OI B-Scan displays.H f v jWhile several embodiments oiv'the'invntion have'beeni illustrated and described in detail,` it 'is to be. expressly understood that invention is not limitedthereto; v'Various invention aswill Vnow be understood 'by 'thoseskille'd in the art.

What is claimed is:

1. In an apparatus .for determining the propagation time of an ultrasonic wave in traveling between a transducer transmitting said ultrasonic waves and an object retlecting said ultrasonic waves, the combination of variable signal means for generating a range sweep signal of uniformly and cyclically varyu'ng amplitude; circuit means responsive to said range sweep signal for transmitting one of a series of alternate electrical signals during each cycle of saidrange sweep signal, each of said series of electrical signals comprising a plurality of electrical signals .Qf YUniformly and .cyclically -varying freqnencies, alternate elecsisnals .in said series .of electrical Signals varying through odset l*frequency ranges while `maintaining a constant frequency dilereuce Vbetween corresponding por.- tions of .said alternate electrical signals; transducer means connected to said circuit means for converting said series of transmitted electrical signals into a corresponding series of transmitted ultrasonic waves, .said transducer means transmitting said series of ultrasonic waves toward said object andreceiying said ultrasonic waves reected from said object and converting .said received ultrasonic waves into corresponding received electrical signals.; means connected to said circuit means and said transducer means for said received electrical signals with the electrical signals then being transmitted; means responsive to said mixing means for selecting and `amplifying only a Video signal cfa frequency equal to the constant difference freA quency between s aid alternate signals of said series of transmitted electrical signals whereby said selected video signal ,isa function o f the propagation time of said ultrasonic waves in traveling between said transducer and the object'from which reected; addition means for receiving and combining said 4video signals andV said range sweep signal to produce a control range sweep signal having a slope which corresponds to the slope of the range sweep signal when no video signals are present and a slope which isreduced during the time when `a video signal is present; and cathode ray tube means including beam deection means .connected in circuit with said video signal means and said addition means to display video signals in time relationship .with said control range sweep signal, said control range sweep signal being applied to said beam deection control means whereby said video'signal display on said cathode ray tube is compressed in time relations hip with respect to said control range sweep signal.

2. The apparatus as defined in vclaim 1 wherein the cathode ray tube means includes horizontal and vertical deection plates and said video signal is applied to the vertical deection plates and said control range sweep signal is applied to said horizontal deilection plates lcausing the horizontal movement of the beam of the cathode ray means to be reduced in speed during the peniods of time' when the slope of .the .voltage excursions of the control range sweep signall is reduced to compress and intensify the Vvideo signal display with respect t Said .control range sweep signal.

A3,. In 1a nondestructive testing apparatus in which transmitted .nltrasnic waves are reflected by an object and defects therein, said reflected ultrasonic waves indicating the presence of areective vsurface `in said object kand the propagation time .of said ultrasonic waves in traveling between the points of .transmission and reflection being a function of the .depth of said rellective surface in v said object, the y,combinaticn of: means for generating a ,first series .of sawtooth range vsweep signals; circuit means responsiye to :saidiirst series of range sweep signals Yfor generating and transmitting a series :of electrical signals of cyclical varying frequency, alternate electrical signals of said .series of electrical signals being transmitted through one ,of said first series of range sweep signals and varying through a dilerent frequency yrange providing a constant frequency diiference between corresponding Parts of adjacent ,signals sadvsies .of electrical signals; trans.-

ducer means responsive to said series of electrical signals for transmitting toward said yobject aseries of nltrav sonic waves corresponding tofsaid series of transmitted electrical signals, said transducer receivingthe ultrasonic waves reflected from said object and .defects therein and converting said reec'ted and received ultrasonic waves into received electrical signals; scanning means for moy, ing said transducer with respect to said object to said object with said transmitted ultrasonic waves'and for generating a second series of `s a'wtooth' range sweep signals corresponding to the position of said transducer with respect to said object being scanned; means conf nected to said circuit means and Vsaid transducer means for mixing said received series of electrical signals with the electrical signals then being transmitted; means responsive to said mixing means for selecting and amplifying a video signal of a frequency equal tothe ,constant frequency difference between said alternate electrical nals of said transmitted series of electrical signals wherei by said video signal is a function of the .propagation time of said ultrasonic waves in traveling between said l,tr-arts'- ducer and said object and the defects thereinffrom which reilected; addition means for receiving vand combining said video signal and said rst senies of range ,sweep signals to produce a control range sweep signal having slope corresponding to the slope of a rst range sweep signal when no video signals are present and .a'slope which is reduced during the time when a video signal is present; and a cathode ray tube including horizontal ,and vertical deflection plates and a control grid `connected in circuit with said video signal means, and said scanning means, said cathode ray tube for displaying `said video signal :in time relationship with said control range sweep signal and said second range ysweep signal being connected to said horizontal deflection plates and said video signal being applied to said control grid whereby said video signal display on said .cathode ray tube is compressed in time relationship with respect to said control range sweep signal, and said video signal applied to -said control grid provides for intensity modulation of .said video in time Yrelationship with respect to said control andfsaid second range sweep signals to intensify the display'fofV said compressed video signal.

4. Apparatus as dened inv laim l, wherein vthe addi?. tion means comprises kan wimpedance network.

5. Apparatus as dened in claim 4 in which the pedance network is a resistive network.

6. Apparatus as defined in claim 3 V in which the ,addition means comprises an impedance network. l

7 Apparatus as de ned in claim 6 in which the pedance network is a resistive network;

References .Cited in the le of this patent UNITED STATES PATENTS 

